‘79 v ‘80 GS 850 cylinder head differences

[sarathchandars]

For my 79 GS850 I’m looking to change the cylinder head because the 3 of the 8exhaust bolt holes are stripped and the previous owner had jb-welded some studs improperly in 2 of them. While I look to clean it up with the current head, I found a good chap selling his 1980 gs850 head. While I know that the cam chain tensioner is the 2 screws v. 3 screw design, are there any other differences that will prevent me from replacing the ‘79 with a ‘80 head?

[Nessism]

'79 heads designed for VM carbs. '80 uses larger Mikuni BS/CV carbs. The port size and intake boot bolt pattern is different.

And to my knowledge, the '79 850 head is the same as the'76-'79 750 head.

[Burque73]

I have a '79 850 head. No broken bolts. Came from a non running parts bike so may need to be refreshed.

PM me if you're interested.

[Nessism]

I have a '79 850 head. No broken bolts. Came from a non running parts bike so may need to be refreshed.

PM me if you're interested.

Bingo! Buy that man a beer! Make it two!

[sarathchandars]

I have a '79 850 head. No broken bolts. Came from a non running parts bike so may need to be refreshed.

PM me if you're interested.

Thanks for the offer. PM-ing you now.

[Burque73]

Thanks for the offer. PM-ing you now.

Got your PM. Hopefully $100 shipped sounds fair. This package weighs over 40lbs so most of the cost is shipping.

Here are some pics of this head. Doesn't appear to have any burnt valves, lots of carbon and junk to clean up though. The bike sat for 10+ years and bottom end was seized so I pulled the head and scrapped the jugs and crank case.

When you asked for advice in your PM about how to get it ready I figured I'd post it here just in case someone who knows better wants to chime in. A lot of what you'll need to do is here on Bwringer's site you should also download a shop manual from here. I had an extra Clymer manual so threw it in the box for you. Sometimes the manuals have different methods of doing things.

The tachometer drive is still on it. I'd plan on ordering a new seal and O-ring, possibly a drive gear. These always leak at some point.

Valve seals probably need to be changed and valves lapped. You'll need a valve spring compresser and valve lappiing tool. There are redneck workarounds for homemade tools which work just fine.

Tappet / valve lash/ valve clearance is an important one. There are shims in every bucket on this head, but please verify clearance. Had an extra tool on hand so I threw it in the box as well. I removed the cams because I thought someone else wanted them so you'll need to look up the torque spec and torque down the cam clamps, a little blue locktite is probably a good idea there. I have no idea if the PO had the clearance set correctly. It will change a little bit if you lap valves and cut the seat at all. Get a good set of feeler gauges for clearance and a micrometer to measure shims.

The rubber half moons on the head are probably shot. Avoid the hassle and change them now.

Breather gasket and valve cover gaskets are a must.

I'm sure there's more to do than all this but hope it helps.

20241229_103620 by Roger, on Flickr

20241229_103808 by Roger, on Flickr

20241229_103709 by Roger, on Flickr

20241229_105357 by Roger, on Flickr

20241229_105322 by Roger, on Flickr

20241229_105924 by Roger, on Flickr

[sarathchandars]

Just saw the photos. The forum notifications didn’t consolidate the response. I’m ok with $100 given that I don’t have options and genuinely I believe you are being fair. Please let me know if I can pay using Venmo as I don’t have a PayPal account.

separately, do you have other parts that I can take off of your hands that you think may be useful?

[sarathchandars]

I guess I owe you a beer or two as Ed mentioned you are a saviour. Now I feel like I should get this bike running for all the goodwill that folks on the forum are showing me.

[Burque73]

LOL, can't turn down a beer (or two)

I have crash bars, forks, calipers front and rear, shocks, clutch lever, side covers and tail cowl, brake light and fender, ignition switch and helmet lock, a nice comple exhaust system and a few more bits and pieces.

Yes, venmo is fine.